private void AsyncUploadParts(String objectName, String fileToUpload,
            String uploadId, int partSize)
        {
            var fi = new FileInfo(fileToUpload);
            var fileSize = fi.Length;
            var partCount = fileSize / partSize;
            if (fileSize % partSize != 0)//count part
            {
                partCount++;
            }

            var ctx = new UploadPartContext()
            {
                ObjectName = objectName,
                UploadId = uploadId,
                TotalParts = partCount,
                CompletedParts = 0,
                SyncLock = new object(),
                PartETags = new List<PartETag>(),
                WaitEvent = new ManualResetEvent(false)
            };
            try
            {
                for (var i = 0; i < partCount; i++)
                {
                    var fs = new FileStream(fileToUpload, FileMode.Open, FileAccess.Read, FileShare.Read);
                    var skipBytes = (long)partSize * i;
                    fs.Seek(skipBytes, 0);
                    var size = (partSize < fileSize - skipBytes) ? partSize : (fileSize - skipBytes);
                    var request = new UploadPartRequest(bucketName, objectName, uploadId)
                    {
                        InputStream = fs,
                        PartSize = size,
                        PartNumber = i + 1
                    };

                    client.BeginUploadPart(request, UploadPartCallback, new UploadPartContextWrapper(ctx, fs, i + 1));

                }

                ctx.WaitEvent.WaitOne();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }
        }



        private void UploadPartCallback(IAsyncResult ar)
        {
            try
            {
                var result = client.EndUploadPart(ar);
                var wrappedContext = (UploadPartContextWrapper)ar.AsyncState;
                wrappedContext.PartStream.Close();

                var ctx = wrappedContext.Context;
                lock (ctx.SyncLock)
                {
                    var partETags = ctx.PartETags;
                    partETags.Add(new PartETag(wrappedContext.PartNumber, result.ETag));
                    ctx.CompletedParts++;
                    Console.WriteLine("finish {0}/{1}", ctx.CompletedParts, ctx.TotalParts);

                    if (ctx.CompletedParts == ctx.TotalParts)
                    {
                        partETags.Sort((e1, e2) => (e1.PartNumber - e2.PartNumber));
                        var completeMultipartUploadRequest =
                            new CompleteMultipartUploadRequest(ctx.BucketName, ctx.ObjectName, ctx.UploadId);
                        foreach (var partETag in partETags)
                        {
                            completeMultipartUploadRequest.PartETags.Add(partETag);
                        }

                        var completeMultipartUploadResult = client.CompleteMultipartUpload(completeMultipartUploadRequest);
                        Console.WriteLine(@"Async upload multipart result : " + completeMultipartUploadResult.Location);

                    }//complete
                }
            }

            catch (Exception ex)
            {

                Console.WriteLine(ex.ToString());
            }
        }